The long term goals of this project are to quantitatively assess changes of structure and material properties in the intervertebral disc (IVD) anulus fibrosus (AF) for longitudinal, in situ monitoring of IVD disorders associated with aging, degeneration, and injury, and to develop physically realistic models of the IVD to accurately predict the origin and evolution of material failure of the disc. Disorders of the IVD are the most frequently diagnosed musculoskeletal conditions in the US, with more than 4 million cases reported annually for people between ages 25-74. Gross AF structural changes, including tears, bulging, and disorganization of the fibrocartilagenous lamellar network, are important diagnostic parameters of IVD disorders. Because the collagen fiber structure is an important determinant of AF mechanical behavior, structural irregularities such as discontinuity of AF lamellae have been identified as a risk factor for disc disorders. Precise in situ information of AF architecture will not only improve the diagnosis of IVD disorders, but will also directly impact on the understanding of structure-function relationships and their alterations associated with pathology via the development of morphologically accurate mechanical models of the AF. However, currently available X-ray diffraction and light microscopy methods for assessment are limited by poor spatial resolution and the destructive nature of the technique. Conventional magnetic resonance (MR) imaging reflects largely tissue compositional and water content changes, which may take more than 12 months after the original structural defect to manifest. The proposed project is centered on the hypothesis that the anisotropy of water diffusion determined by MR diffusion tensor microscopy is sensitive to changes of structure and function in the AF associated with intervertebral disc degeneration. To address methodological aspects of the long term goals, the specific aims of this pilot study are to: (1) develop dedicated MR microscopy pulse sequences and acquisition strategies for performing three-dimensional diffusion tensor microscopy of the AF, (2) perform direct correlation of the collagen fiber structure determined by MR diffusion tensor microscopy and established histological techniques in excised AF samples. AF, (3) correlate morphology-based predictions and direct measurements of AF tensile properties in excised AF samples, and (4) quantify and compare morphological features of the AF in vitro for non-degenerate, mild, and severe grades of degeneration.